Method of making printing plates



Oct. 5, 1937. D" L055 ET AL 2,095,071

METHOD OF MAKING PRINTING PLATES Filed April 7, 1956 W/f/VL-SS: fiaviaS. Last;

Ian/6: @7265 M 7 0267 Patented Oct. 5, 193? V UNITED STATES PATENTOFFICE,

METHOD OF MAKING PRINTING PLATES David S. Loeb and James M. Toler,Philadelphia, Pa.

Application April 7, 1936, Serial No. 73,060

,1 6 Claims. (01. 153-32) This invention relates to a method of makingFig. 4 is an end elevation showing the plate printing plates andspecifically to a process of after it is curved and backed with paper;and

forming zinc plates suitable for use on a multi- Fig. 5 is a perspectiveview showing the finished graph machine or other rotary printing machineplate applied to a multigraph drum. 7 5 directly from a flat zincengraving. Heretofore There is indicated at 2 in Fig. l a fiat zinc 5the common practice pursued in forming cylinengraving formed of asuitable zinc alloy and drical printing surfaces for use on multigraphwhich has been prepared in conventional fashion. machines or the likehas involved the formation This engraving is provided with flanges i and6 of a flat zinc engraving from which there was for reasons mentionedhereafter, and is prov 10 formed a matrix of wood pulp paper. This videdwith relief printingsurfaces indicated at 10 matrix was then bent to thedesired curvature 8. If the original engraving contains any large andstereotype metal cast therein to form the areas which are in the natureof depressions and final printing plate. The old process has merelywhich are therefore comparatively thin and unrebeen outlined and was farmore complex than the inforced bythe relief printing surfaces, forexamoutline would indicate. As a consequence, the ple such as indicatedat iil,such low parts andalso l5 printing plates so formed were quiteexpensive. the flanges may be packed withstereotypepacking Furthermore,the process was not particularly prior to the bending step. Thestereotype packing well adapted to fine work. consists of cardboardprovided; in various thick- The rather obvious solution to the problemapnesses which may be secured in the low parts of peared to be thebending of the zinc engraving the face of the engraving by means ofglue. Such O into the proper curvature to act directly as the packing isfound desirable where considerable printing surface and many attempts todo this low areas exist in order to avoid buckling which 7 were tried bythe use of heat and pressure in varimay take place in the relativelythin areas correous ways. The results, however were never satisspondingthereto.

factory, inasmuch as the attempts at bending Zinc engravings arenormally of sixteen gauge 5 always resulted in damage to the printingsurand if applied directly to a multigraph drum will face. be below typelevel. Thirteen gauge zinc en- It is a general object of the presentinvention gravings would be type high. However, it is de-' to provide aprocess whereby flat zinc engravings sirable to use sixteengauge'engravings not only or similar flat printing plates, such as stereotypebecause, being standard, they are cheaper since 30 plates, or the like,may be curved to directly prothey can be handled in usual fashion, butalso vide a printing plate and more specifically in such because theboard which is used to back them to fashion as to eliminate entirely orminimize the make them type high is resilient and automatimake-readywhich is necessary. The process has cally provides for automaticadjustability, which been found excellently adapted to all types ofgreatly minimizes the make-ready which is-necesg engraving, includingline and half-tone engravsary. The process will consequently bedescribed ings, fine screen engravings, and engravings of as applied toa sixteen gauge zinc engraving for combination types. It is particularlyadapted to use on a multigl machine'- the formation of printing platesfor multigraph A- furnace I2" heated by burners M is' provided 40machines to be used either alone or in conjunchaving an external surfacewith a curvature the 40 tion with type, the plates for this purposebeing same as that of the multigraph drum to which formed from zincengravings which are composed the plat be p This furnace/is p e e f nknown Zinc alloys; ably provided with a flangearrangement indi- Thebroad object. of the invention and also subd f d'esiged to r e e a 1 upsidiary objects relating to details of construction edge i rfi w 5'51: gwill be apparent from the following description element 9 th l surface,F Dartmouread in conjunction With the accompanying drawlarly deslrableprqvlde u l flagge mg in which: inasmuch as otherwise a, slight error nlocat ng the plate on the furnace may result in skewing Fig. 1represents in perspective a flat z1nc ento an, uneorrectable extent. fwhwh the 15 to be apphed; A particularly distinctive feature of theprocess F 'ig- 2 1s a perspect Ve V Of a furnace Over herein describedisthe proper heating of the. whlch the plate 18 curved; zinc engravingduring the" bending process. The V Fig. 3 is a fragmentary elevation ofa press in zinc engraving at ordinary temperatures" is quite which theplate is given its: final shape; resilient and while it maybe benttothe" desired '55 'When the entire plate is'curved .aboutthefurscribed, no damage is done to the engraved' surg face. q

After the bending} is completed. the curved V radius ofciiivaturaifsucibenditg occurs about a surface having that curvature the plate will 7spring to acond'itioh of less curvature as'soon as the pressure isreleased. 7 At' the same time, it will have been strainedbeyond itselastic limit V i and, .inasmuch as the printing surface is outsidedamage will almost invariably occur." 7

'Typical zinc=engraving plates'melt jat about 7' 7809 F. 'and'quite"substantially, soften well below I Ethatjtemperature. It is'found,however, that by heating the plate above ;2 50F., and preferably between300 Ffto 500 F.,;theaplatef becomes pliable and loses its resiliencywithout; however;

there being any danger'of damaging the engraved; surface. .It mayberemarked that the temper ,ofthe plate is considerably removed duringthel heating, which occurs in conjunction with the etching process, sothat if 'the'plate has a; hard- "ness,.measured by the sclero'scope, of.26 points before it is etched, it finally has a hardness 'of onlylfi-pointswhen finished in flat form; When heated'in the range of 300 to500 E, its hardness drops to approximately 5 points orrless, but

the hardness cooling.

V 7 Assuming that'the: furnace ha'si been heated. .to secure the desiredtemperature of the plate as indicatedabove, the plate is. applied tolthe r r (furnace 12 with oneedge engaged by'the flange -the' flange maybeomitted andthe plate applied I6, 'th'ough it will be understood thatwith skill tofthe; furnace along-a straight ,line' element thereof andthen bent, as will be now described.

After application; of the plate ,to the furnace, 'moder'ate pressurerisapplied thereto to cause it i to conform gradually with the curvature ofthe furnace. In the case, of a 65 gauge pIate the 1 weight of theoverhanging portion of the plate The bending must'be so performed,however, T that at no time islany portion of the plate bent V isgenerally insufficient and some slight extra pressure must be applied tocause it to bend.

which has not attained the temperature indi-.

. cated above. Since the temperatureof the plate. 7

. diminishes through the portionwhich is not in is' maximum, where itengages the furnace and engagement with the furnace, it will be clear Ythat. the'bending process takes place progressively, as indicated inFig. 2, the successive portions of the plate bending as they lose'theirresiliencyfat the temperature I of s the furnace.

nace, it has no tendency to spring away from I the furnace, at ;least toany substantial degree.

By the progressive bending'which has been de plateis immediately removedto a press ltcona taining a depression, lined with a copper sheet,indicatedat 20, the inner surface of which has exactly the curvature ofthe printin Surface desired on the completed'plate. The male 'member 22of the press is provided with a pressure 65 surface, which has thedesired =inner curvature. The plate located between the two pressure sur.faces'is then pressed by means of a screw and nut arrangement indicateddiagrammatically at 24 .1 The soft copper :lining is" provided to avoiddamage to the engraved surface during "the 2 pressing operation; itbeing softer than the; zinc alloy, This preliminary 'pressing 'whiletheplate is still hot is necessary. to insure'the precise cur,-

'vature'which 'isydesired, inasmuch; as this can only; be; approidmatedon the furnace. Alter-1 V 2,095,071 i r I s V natively, of course, apressure member might be] of 15 pointsfis regained upon provided abovethe furnace to press the plate on its surface, which is formed with acurvature r corresponding to the desired inner curvature of V 'theplate. The cooling in such case is slow since the 'entire, furnace mustbe allowed to' cool.] j

After removal from the press, any paper pack- I in warm water andscrubbing. w r The'curved plate is now backed by'pasteboard" ing used inthe. low spotsis removed by soaking. j

2 6 which is secured to the plate byjpastef The" laminated structurethusobtainedis returned to r the press I8 and repressed' to insure that both:5 J

the finnerjandouteri curvatures are correct and} f to secure uniformadherencefofthe paper to the ,gplate. Only a slight pressureis used atthis time to avoid squeezing up the low portionswhich might make ther'n'print. Q

,The finished plate'is now readyfor application tothe cylinder indicatedat 28, which may,'for

example, be the slotted cylinder of a'multigraph V board '26, together:with the bending process which has been usedand which avoids dam-age tothe engraved surface, goes far toward eliminating the necessity formake-ready. If it is found,

however, that the first proofs are unsatisfactory,

the usual make-ready procedure may beadopted" and paper secured underthe low portionsof the plate so as to cause them to print to,the'properdensity. SandpaperingLof the backing board,

under high portions will serve to correct them. V

It. is found, however, that generally little orfno make-readyisnecessaryto secure good results.

7 The process described herein is applicablenot f only to zinciplatesbutalso other types such as stereotype and electrotype plates. ofstereotype plates somewhat greaterfcar e-.must

In'the case be exercised since the metal melts "atla consid;

erably lower point than the zinc alloy and the 1 range of temperaturesinwhich the bending'may be properly effected is more limited. 'In handling .such'plates, it ,is desirable to cover the surface of the furnacew'ith asbestosror some other relatively poor conductor of heat was islower transmission'to the plate. tions in procedure may ous othermaterials;

Similar variaadopted to suit vari It will be obvious thatichanges indetails'of the process may be 'adopted'without departing:

from the invention herein described- N r I What we claim and desire toprotect by Letters Patentisz' '1 I 1. The process of forming a-curvedprinting plate from a flat printing plate including heating acylindrical surface toQatemperature at which the plate would benon-resilient but belowthe melting point ofthe' 'plate,"applying.theback of the flat plateto said heated cylindrical sure facealong astraight lineelementofthe'surface;

to'secure a better distribution of the heat and exerting a bending forceupon portions'ofithe plate remote from the region of contact of theplate and cylindrical surface; while avoiding-ii rect pressure on theouter faceofthe portions :1 r

being bent, to eifect a gradual progressive con .formity of the platewith the heated surface as portions of the plate adjacent those incontact with the surface are progressively heated to said temperature,the bending force being so moderated that bending to the curvature ofthe surface takes place only at the portions of the plate progressivelyheated to a temperature at which they are non-resilient, and thereafterpressing the curved plate while still hot in a press having pressuresurfaces corresponding to the desired inner and outer surfaces of thefinal curved plate.

2. The process of forming a. curved printing plate from a flat printingplate including heating a cylindrical surface to a temperature at whichthe plate would be non-resilient but below the melting point of theplate, applying the back of the flat plate to said heated cylindricalsurface along a straight line element of the surface, exerting a bendingforce upon portions of the plate remote from the region of contact ofthe plate and cylindrical surface, while avoiding direct pressure on theouter face of the portions being bent, to effect a gradual progressiveconformity of the plate with the heated surface as portions of the plateadjacent those in contact with the surface are progressively heated tosaid temperature, the bending force being so moderated that bending tothe curvature of the surface takes place only at the portions of theplate progressively heated to a temperature at which they arenon-resilient.

3. The process of forming a curved printing plate from a fiat printingplate including heating a cylindrical surface to a temperature at whichthe plate would be non-resilient but below the melting point of theplate, applying the back of the flat plate to said heated cylindricalsurface with an edge. of the plate contacting a straight line element ofthe surface, exerting a bending force upon portions of the plate remotefrom the region of contact of the plate and cylindrical surface; whileavoiding direct pressure on the outer face of the portions being bent,to effect a gradual progressive conformity of the plate with the heatedsurface as portions of the plate adjacent those in contact with thesurface are progressively heated to said temperature, the bending forcebeing so moderated that bending to the curvature of the surface takesplace only at the portions of the plate progressively heated to atemperature at which they are non-resilient, and thereafter pressing thecurved platewhile still hot in a press having pressure surfacescorresponding to the desired inner and outer surfaces of the finalcurved plate.

4. The process of forming a curved printing plate from a flat printingplate including heating a cylindrical surface to a temperature at whichthe plate would be non-resilient but below the melting point of theplate, applying the back of the flat plate to said heated cylindricalsurface surface, while avoiding direct pressure on the outer face of theportions being bent, to effect a gradual progressive conformity of theplate with the heated surface as portions of the plate adjacent those incontact with the surface are progressively heated to said temperature,the bending force being so moderated that bending to the curvature ofthe surface takes place only at the portions of the plate progressivelyheated to a temperature at which they are non-resilient.

5. The process of forming a curved printing plate from a fiat printingplate including heating a cylindrical surface to a temperature at whichthe plate would be non-resilient but below the melting point of theplate, applying the back of the flat plate to said heated cylindricalsurface along a straight line element of the surface, exerting a.bending force upon portions of the plate remote from the region ofcontact of the plate and cylindrical surface, While avoiding directpressure on the outer face of the portions being; bent, to effect agradual progressive conformity of the plate with the heated surface asportions of the plate adjacent those in contact with the surface areprogressively heated to said temperature, the bending force'being somoderated that bending to the curvature of the surface takes place onlyat the portions of the plate progressively heated to a temperature atwhich they are non-resilient, and thereafter pressing the curved plateto accurate curvature.

6. The process of forming a curved printing plate from a flat printingplate including heating a cylindrical surface to a temperature atwhichthe plate would be non-resilient but below the melting point of theplate, applying the back of the flat plate to said heated cylindricalsurface along a straight line element of the surface, exerting a bendingforce upon portions of the plate remote from the region of contact ofthe plate and cylindrical surface, while avoiding direct pressure on theouter face of the portions being bent, to effect a gradual progressiveconformity of the plate with the heated surface as portions of the plateadjacent those in contact with the surface are progressively heated tosaid temperature, the bending force being so moderated that bending tothe curvature of the surface takes place only at the portions of theplate progressively heated to a temperature at which they arenon-resilient, applying a paper backing to

